Domestic appliances may be powered by split-phase (240V) or three-phase (208V) alternating current (AC) power supplies that are miswired at the outlet, the power cord, or internal to the appliance, potentially causing damage to or malfunction in the appliance. Typically, light electrical loads, such as fans, lights, and displays, are powered by a single 120V side (L1 leg) of a split-phase supply, whereas heavy electrical loads, such as a heating element, are powered at 240V between two hot lines (L1 and L2). One solution to the risks of miswiring can be found in prior art reference U.S. Pat. No. 8,781,784 (“System and method for detecting miswiring of an electrical appliance”) where all appliance loads are disconnected when a phase difference between supply hot lines L1 and L2 is detected to be 0 degrees. Unfortunately, a phase difference of 0 degrees occurs when either the L1 or L2 hot lines and the neutral line are reversed, causing light electrical loads powered on the L1 side to be unnecessarily disabled in the case of the low-risk scenario of L1 and neutral being swapped. The user is then left without fans, lights, and/or displays in situations where they could be safely provided.
Also, the technique in the prior art of using a zero-degree L1-L2 phase difference to disable all electrical loads may prevent lights and display from operating in a showroom demonstration where the L1 supply may be wired to feed both L1 and L2 of the appliance input. Intentional rewiring may be necessary when 240V power supplies are not practically available on a showroom floor, but it remains desirable to demonstrate the lights and display of an appliance. Further, the prior art use of a zero-degree phase relationship may yield a false positive in the case of a three-phase 208V power supply, where 2 of the utilized hot lines are 120 degrees offset from each other, and the swapping of a hot and neutral line yields a 30 degree or 330 degree offset between L1 and L2. In this case, a dangerous miswire condition may occur yet the prior art may fail to disconnect the heavy electrical load.